1. Field of the Invention
This invention relates to a cleaning blade in pressing contact with the surface of an electrostatically charged latent image support and for removing toners remaining on the surface, the cleaning blade being used in an image-forming apparatus such as electrostatic copying machines, printers, and facsimile apparatuses and also in apparatuses using the cleaning blade.
2. Related Background Art
Electrophotographic apparatus for forming an image by transferring a toner image on the surface of an electrostatically charged latent image support to a transfer material includes, for example, copying machines, laser beam printers (LBP) and facsimile apparatuses.
The electrophotographic process will be explained below,
The surface of a photosensitive member as an electrostatically charged latent image support is negatively charged by a charging means and then subjected to image scanning by exposure to a laser beam as a latent image-forming means, thereby forming digital latent images on the surface of the photosensitive member, Then, the electrostatic latent images formed on the surface of the photosensitive member are developed with toners to form toner images, and the toner images are electrostatically transferred to a transfer material. The electrostatically transferred toner images on the transfer material are fixed by a fixer as a fixing means to form fixed images on the transfer material.
On the other hand, the toners remaining on the surface of the photosensitive member after the transfer step are removed by cleaning with a cleaning means having a cleaning blade. After the removal of toners by cleaning, the photosensitive member is discharged by erasing light exposure and then repeatedly used in the electrophotographic process starting with the charging step.
When the removal of toners from the photosensitive member by cleaning with a cleaning blade is incomplete, succeeding latent images are formed while the toners remain on the photosensitive member, and thus parts of the formed latent images drop off.
The cleaning blade is a plate-shaped molding product made mainly from a polyurethane elastomer and works to physically remove toners attached to the surface of a photosensitive member by cleaning through contact therewith. In that case, the blade must overcome the electrostatically attractive force of toners attracting the toners toward the surface of the photosensitive member to remove the toners from the surface of the photosensitive toner, and thus the blade must be pressed onto the surface of the photosensitive member with a large pressing force. That is, a large frictional force develops between the photosensitive member and the cleaning blade, and the cleaning blade is turned up and reversed, resulting in a failure in the rotary movement of the photosensitive member or in the cleaning. When the surface of the photosensitive member is soft, the surface is considerably scraped, resulting in poor images or a shortened life of the photosensitive member. Particularly at the initial period, coagulation takes place between the surface of the photosensitive member and the cleaning blade, because of the smooth surface of the photosensitive member, and thus the cleaning blade is more liable to turn up.
To solve these problems, various improvements have been so far proposed. Powder of fluorocarbon resins such as PTFE and PVDF is applied to the edge of a cleaning blade to prevent the initial turn-up of the cleaning blade. However, the powder of fluorocarbon resins is retained on the surface of the cleaning blade only through a weak electrostatic interaction, and thus is very likely to disengage from the surface of the cleaning blade during the working. When the photosensitive member is charged while the disengaged powder of fluorocarbon resins remains on the photosensitive member, the fluorocarbon resins are abnormally charged to retain an electrical memory on the photosensitive member, resulting in poor images.
When a charging system for bringing a roller-shaped charger into contact with the surface of a photosensitive member is used in place of a primary charger for conducting ordinary corona charging as a system for charging the photosensitive member, the powder of fluorocarbon resins disengaged from the cleaning blade is filled in the space between the photosensitive member and the contact-type charger, resulting in poor charging or the powder is deposited onto the contact-type charger, resulting in poor charging. Thus, there are problems such as the formation of poor images.
As an alternative, coating of the surface of the cleaning blade with polyamide resin such as nylon is proposed [Japanese Patent Application Kokai (Laid-Open) No. 59-52273], where the frictional coefficient can be lowered but is still not satisfactory, and since the surface of the photosensitive member is smooth particularly at the initial stage, coagulation with the surface of the cleaning blade takes place, making the blade turn up or the coating layer peel off or become defective. Furthermore, the surface of the electrostatically charged latent image support is sometimes scraped off during prolonged operation.
As another process, Japanese Patent Application Kokai (Laid-Open) No. 49-11704 (corresponding to U.S. Pat. No. 3,936,183) discloses a cleaning blade comprising a polyurethane sheet and a coating layer formed on the surface of the polyurethane sheet, the coating layer containing fine powder of inorganic lubricant material such as graphite fluoride or organic lubricant material such as polyvinylidene fluoride, using a resin material such as polyurethane, epoxy resin, phenol resin or alkyd resin as a binder for the coating layer. However, the resin material used as a binder for the coating layer is not better in both lubricability and wear resistance, and when the cleaning blade is used in an electrophotographic apparatus to clean the surface of the photosensitive member to remove the remaining toners therefrom, the binder resin is worn out and the fine lubricant powder drops off the coating layer, resulting in the incomplete removal of toners.